A number of problems in photonic crystal laser cavities have been observed. These problems are related to the unique geometry of photonic crystal lasers, which require small features to be etched through active material to define mirrors and cavities lithographically. The small dimensions of the etched features leads to potentially large surface recombination losses. Moreover the same material that generates light in optical cavities also constitutes the etched regions that reflect the light, resulting in light re-absorption losses. Finally, these lasers are often fabricated within thin membranes with little thermal heat-sinking, and have been mainly demonstrated in materials with low bandgaps, and this leads to high Auger recombination losses. Nonetheless, photonic crystal cavities offer many advantages over more conventional cavities for achieving ultrasmall modal volumes while maintaining high quality factors. When combining such cavities with light emitting active materials, such as quantum wells (“QW”) or quantum dots (“QD”), it is possible to define ultra-small lasers. Such lasers are particularly interesting for applications in optical data communication. Past research on photonic crystal lasers has focused on near-IR wavelength emission using InGaAsP or InGaAs active materials.
In “Two-dimensional photonic band-gap defect mode laser,” Science 284 (5421), 1819-1821 (1999), O. Painter, Jr. K. Lee; A. Sceherer et al. described a laser cavity formed from a single defect in a two-dimensional photonic crystal. The optical microcavity consisted of a half wavelength-thick waveguide for vertical confinement and a two-dimensional photonic crystal mirror for lateral localization. A defect in the photonic crystal was introduced to trap photons inside a volume of 2.5 cubic half-wavelengths, approximately 0.03 cubic micrometers. The laser was fabricated in the indium gallium arsenic phosphide material system, and optical gain was provided by strained quantum wells designed for a peak emission wavelength of 1.55 micrometers at room temperature. Pulsed lasing action was observed at a wavelength of 1.5 micrometers from optically pumped devices with a substrate temperature of 143 Kelvin.
In “Quantum dot photonic crystal lasers,” Electronics Letters, 38 (17), pp. 967-968, (2002) T. Yoshie, O. B. Shchekin, H. Chen, D. Deppe, and A. Scherer described coupled cavity designs on two-dimensional square lattice photonic crystal slabs that were used to demonstrate optically pumped indium arsenide quantum dot photonic crystal lasers at room temperature. Threshold pump powers of 120 and 370 μW were observed for coupled cavities including two and four defect cavities defined in optimized photonic crystals.
Other groups have explored devices capable of emitting visible light. For example, in “Fabrication of photonic crystals for the visible spectrum by holographic lithography”, Nature 404 (6773), 53-56 (2000), M. Campbell, D. N. Sharp, M. T. Harrison et al. described a technique of three dimensional holographic lithography well suited to the production of three-dimensional structures with sub-micrometer periodicity. In “Ultraviolet photonic crystal laser,” Applied Physics Letters 85 (17), 3657-3659 (2004), X. Wu, A. Yamilov, X. Liu et al. described two-dimensional photonic crystal structures in zinc oxide films with focused-ion-beam etching. Lasing was realized in the near-ultraviolet frequency at room temperature under optical pumping. In “Visible resonant modes in GaN-based photonic crystal membrane cavities,” Applied Physics Letters 88 (3), (2006), C. Meier, K. Hennessy, E. D. Haberer et al. demonstrated fabrication of fully undercut GaN photonic crystal membranes containing an InGaN multi-quantum well layer. It has remained difficult to obtain small mode volume lasers in visible light emitting materials systems, due to high surface carrier recombination velocities or the lack of high refractive index contrast substrates for light confinement in the vertical direction.
There is a need for efficient visible light emitting lasers and detectors.